The present invention concerns a painting system comprising a paint booth and a robot installation for painting large objects inside the painting booth. More particularly, the invention concerns such a painting system including a paint booth with walls isolating the object to be painted from the surroundings. Still more particularly, the invention concerns such a system wherein the robot installation contains an industrial robot having at least four axes for servo-controlled movement. An industrial robot in this context comprises a manipulator with electric motors and a control means containing power means for driving the motors and a computer that performs instructions of a computer program to sense and control the manipulator movements.
Painting of car bodies on an industrial scale usually takes place in a painting booth, through which the car bodies are moved on a conveyor in a line succession. For example painting of car bodies in such booths, simple type of hard automation solutions as reciprocators or the like are used. Apparatus of this type may have a sufficient range of reciprocal motion in the vertical direction, but have rather limited ranges of motion in the transverse direction of the painting booth, and practically no option for tracking the object to be painted in the direction of the conveyor motion through the booth. Several such reciprocators having overlapping working ranges along the length of direction of the booth must then be used to maintain a reasonable conveyor speed and paint coverage. A typical representation of prior art machines of this type are shown in FIGS. 1 and 2.
In order to obtain an optimal and uniform layer of paint and an optimum painting quality, the paint must be sprayed from the painting tool in a controlled manner normal (perpendicular) to the surface to be covered. The motion pattern of the painting tool must then be correspondingly programmed in relation to the curved surfaces and edges of the car body. This can only be accomplished by means of flexible solution including a plurality of industrial robots. The robot can easily adapt the paint tool to the optimal path pattern for the different car models, which are produced/painted in the same production line. Such robot solution must then be located in the paint booth itself, which requires considerably wider booths than would be needed in an optimal production line. A typical view of a prior art paint booth with a plurality of industrial robots for painting a large object is shown in FIG. 3. Another painting apparatus of this kind is known from U.S. Pat. No. 4,714,044.
From U.S. Pat. No. 4,630,567 a spray paint system including a paint booth is previously known. The system comprises two painting robots that are moveable on rails along a car body in the direction of the conveyor movement of a car stream. The known system discloses a booth with wall defining the enclosed painting area and at least one painting robot located inside this painting area. The painting robot is moveably supported on a track means outside of the painting area. Track means comprising rails however are costly and very delicate in function on dirt and particles on the rails. Thus, it is difficult to keep track of the robot position on the rails.
Still all of the known painting systems use a plurality of manipulators on each side of the car body to fully cover the whole area to be painted. The more manipulators inside the painting booth necessary for painting the object the higher the investment costs. A larger number of manipulators to be controlled to simultaneously paint the object normally results in a very complex software programming.
A commonly known upright mounted industrial robot has a stand rotatably arranged around a vertical axis. The stand carries a lower arm rotatably arranged around a horizontal axis and the lower arm carries an upper arm also rotatably arranged around a horizontal axis. In order to reach full operational capacity, the robot needs a clearance between the robot and the back wall to permit the maneuvering of the lower arm. On the other hand, the paint booth itself must be as small as possible. Thus, there is a conflict of demands. The robot needs more space and the booth must be restricted in volume. One way to handle this situation is to arrange a plurality of robots arranged with overlapping operation areas and so operating that the lower arm never swings backwards. Thus, in such systems there is no need for a maneuvering space behind the robot. This arrangement of course affects the performance of the robot. The robot then is only capable of making short paint strokes. An increased number of short paint strokes calls for an increased number of time-consuming re-orientation operations and severe waste of paint.
Consequently, there is a need within the industry of car manufacture to decrease the space demands for a paint booth and still increase the operation capacity of the painting robots to maintain or even increase the production volume.